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The paper is concerned with the thermal fatigue testing of sheet metal carried out over a number of years. The test program was first embarked upon when cracks, which were not thought to be due entirely to mechanical fatigue, were found at the edges of holes in sheet-metal flame tubes.
A thermal fatigue test was devised based on heating a test specimen with a central hole to 1650 F and then cooling it rapidly in a blast of cold air. The thermal cycle was based on the temperature curve taken on a flame tube on an engine during accelerating and decelerating conditions.
The early work was concerned with Nimonic 75—a nickel-chromium alloy used for flame tubes on most British engines—and showed the relationship between increasing thickness of sheet and thermal fatigue life and also the temperature-life relationship of this material. The program was then widened to include other nickel-base alloys; austenitic and duplex stainless steels; mild and low-alloy steels (protected from corrosion); and laminated materials.
Lardge, H. E.
Materials Laboratory, Joseph Lucas (Gas Turbine Equipment) Ltd., Wood Top, Burnley,